Exciter light for sound recorders



' July 1s,- 1939. v J D, STACK 2,166,186-

EXGITER LIGHT FOR SOUND RECORDERS Filed Dec. 4, 1937 q as 51 35 1 5?.

Fug. 2. 28 \is INVENTOR. John D- Stack BY ATTORNEY.

M44 K [@M (y Patented July 18, 1939 UNITED STATES PATENT OFFICE John David Stack,

LB An Calif., assignor to Twentieth Century-Fox Film Corporation, Los Angeles, Calif., a corporation of New York Application December 4, 1937, Serial No. 178,098 6 Claims. (01. 179-100.3)

This invention relates to the art of sound recording and deals particularly with means for maintaining the efficiency of exciter lamps used in such systems.

The hereinafter described invention refers to a companion application, Serial Number 178,097, filed Dec. 4, 1937, entitled Monitoring means for sound recorders, and also refers to a copending application filed by C. N. Batsel, Serial Number 177,907, filed Dec. 3, 1937, entitled Monitoring system. The above mentioned applications are drawn to cover separate developments in the art of monitoring in sound recording, while the present invention deals with a feature closely related to the same developed art.

In recording sound, either by the variable area method or the variable density method, it is known that an exciter lamp is used as a source of light to be modulated for forming a sound track on a light sensitive film. It is also known that the density formed on the film is proportional to the brilliancy or intensity of the light source. In practice, it is imperative that the film density be held between very close predetermined limits. As a result the intensity of the light source must be maintained at a predetermined fixed value. The type of lamp used ordinarily consists of a coil filament held between two supports. At times one of the coils of the filament may short out and become black. This naturally changes the intensity of the light source and consequently the density on the filament is changed. The change in film density ordinarily appears as a line or zone of difierent density running longitudinally of the track and upon reproduction will introduce objectionable characteristics or it may result in a lowering of the over-all density of the track. In order to avoid introducing such objectionable characteristics I provide means whereby the filament of the exciter lamp may be observed at all times by the operator in charge of the machine so that he may detect immediately any shorted coils and avoid using a lamp with an imperfect filament. The means provided may con- 45 sist of an optical system whereby an enlarged image of the filament is projected directly on to the monitoring screen commonly employed by the operator to observe sound modulation of the system. By placing the image of the filament 50 alongside the sound modulation indications on the conventional monitoring screen it becomes a comparatively simple matter to observe the condition of the filament along with the sound modulation. Accordingly it becomes the objects of 55 this invention to provide an optical system in sound recorders for projecting in an enlarged form the image of the filament of the exciter lamp upon a screen readily visible to the operator. Another object of this invention is to utilize the same monitoring screen that is used for observing sound modulations for observing the condition of the filament. Still another object is to provide an optical system of the character described that may be inexpensively installed upon existing equipment.

Other objects and advantages will become apparent as the description proceeds in conjunction with the drawing in which:

Figure 1 is a schematical diagram of the optical system employed in a certain type of sound recorder showing my invention schematically applied thereto;

Figure 2 is a vertical cross section of the exciter lamp used in this system showing my invention in detail.

Briefly stated the invention comprises a lens arranged to focus the image of the filament of the exciter lamp upon a screen. In order to render the invention more advantageous I use a mirror in the path of the projected image to reflect the image upon the same screen that is used for observing the sound modulation of the system.

Referring to Fig, 1, it will be seen that the optical system of the sound recorder above mentioned comprises an exciter lamp generally designated L. The lamp L contains a filament l I which is ordinarily in the form of a coil and is shown diagrammatically in this view. The image of the filament H is brought to an air focus slightly ahead of a light slit [2 by means of an objective lens I3 and a galvanometer mirror l4, while the image of the light slit I2 is focused upon a film F by another objective lens I 5. The result is that although the image of the filament II is not focused directly upon the film F, any change in light intensity in the length of the filament will efiect the film density and will appear as a line or zone of different density running longitudinally of the track. Or if the air focus be sufficient distance from the slit l 2 the result will be a low ering of the over-all density on the track. For monitoring sound modulation, a part of the light from the filament H is intercepted by a mirror l6 and is projected onto a monitoring screen i! by mirrors l8 and I9 having a lens 2!! in the system. The modulation indications and the noise reduction indication appear in separate tracks disposed at right angles to each other forming a letter L on the card. This part of the invention is more fully disclosed and claimed in a co-pending application filed by C. N. Batsel, Serial Number 177,907, filed Dec. 3, 1937, entitled Monitoring system.

In conjunction with the foregoing my invention provides means for projecting an image of the filament ll upon the same monitoring card I1. Briefly stated the invention comprises a lens 2| arranged to focus the image of the filament ll, upon the card 11, by means of a reflecting mirror 22.

In Fig. 2, I have shown the arrangement of these parts in detail. Here it will be observed that the lamp L, having the filament II, is mounted upon a base 25. No details of the elec trical circuit for supplying the lamp with energy are shown since this is common in the art. The base 25 carries a cylindrical casing 26 which is adapted to surround the lamp bulb and extend slightly above the lamp. Another casing 2! annularly spaced from the casing 26 is supported upon the casing 26 by members 28. The upper end of the casing 21 is closed by a cross member 29 which has an aperture 30 therein, while the casing 26 is open on the upper end. A second member 3| is provided across the upper end of the casing 21 and an opening 32 is formed in this member. Over the aperture 30 and in the opening 32 I mount the lens 2| hereinbefore mentioned by any suitable means such as springs 35. Since it is one of the objects of this invention to project the image of the filament upon the same screen that is used for observing sound modulation I provide the mirror 22 directly over the lens 2| which deflects the ray as desired onto the screen II. The mirror 22 may be mounted upon the plate 3| in any suitable manner, the only requirement being that the mounting is capable of yielding the necessary adjustments for properly positioning the mirror to deflect the rays upon the screen. In this instance I have shown the mirror as being supported upon a rod 33 which in turn is universally supported upon a post 34 carried by the plate 3|. With the foregoing arrangement I am enabled to project the image of the filament l l in an enlarged form upon the card I! where it appears as Ila and becomes easily observable by the operator at all times while he is monitoring sound modulation, thus enabling him to immediately note any dark spots in the filament indicating shorted coils and prevent loss of film and time by replacing the exciter lamp.

An arrangement of the foregoing nature whereby an image of the exciter lamp filament is thrown upon the same screen that shows sound modulation provides an improved means for observing the condition and efficiency of the light source in sound recorders.

I claim:

1. In a sound recorder having a monitoring screen for visually indicating sound modulations; an exciter lamp having a filament therein, and means for focusing an image of said filament onto said monitoring screen.

2. In -a sound recorder having a monitoring screen for visually indicating sound modulation; an exciter lamp having a filament therein, a light proof housing around said lamp, an aperture in said housing above said lamp, a lens mounted in said housing over said aperture, and a mirror mounted on said housing over said lens and adapted to deflect light rays passing through said lens to said monitoring screen.

3. In a sound recorder having a monitoring screen the combination of; means for visually indicating sound modulation upon said monitoring screen, an exciter lamp having a filament therein, and means for projecting the image of said filament upon said monitoring screen.

l. In a sound recorder having a monitoring screen the combination of means for visually indicating sound modulation upon said monitoring screen; an exciter lamp having a filament there" in, and a lens arranged over said exciter lamp and adapted to focus the image of said filament upon said monitoring screen.

5. In a sound recorder having a monitoring screen the combination of means for visually indicating sound modulation upon said monitoring screen, an eXc-iter lamp having a filament therein, an optical system for focusing the image of said filament upon said monitoring screen, said optical system including a lens arranged to pass light rays from said filament and a mirror arranged to deflect said light rays onto said screen.

6. In a sound recorder having a monitoring screen and an exciter lamp with a filament therein the combination of; means for visually indicating sound modulation upon said screen, and means for projecting an image of the filament of said exciter lamp upon said-monitoring screen, said last mentioned means including a lens and a mirror arranged to focus the image of said filament upon said screen.

JOHN DAVID STACK. 

